Sikorsky Aircraft Corp. has won a $435 million contract to build four operational test helicopters for a program to replace an aging fleet of the Marine's heavy-lift transport helicopter.

The Pentagon, in issuing the contract update Thursday, approved this next step in the CH-53K program's $3.5 billion development and demonstration phase, which aims to deliver the first operational helicopter to the Marines in just over three years.

"The Navy and Marine Corps have shown a high level of confidence to the CH-53K team as we move forward on this important next phase of the program," said Sikorsky spokesman Frans Jurgens. "The Marines want another set of aircraft to see if they can do the mission."

Sikorsky is a subsidiary of United Technologies Corp.

The new aircraft is set to replace its older sibling, the Sikorsky CH-53E Super Stallion, which for decades has been the Marines' choice for transportation and cargo delivery. The new CH-53K, from the outside, looks just like the CH-53E, but its specs are three times more powerful due to a new engine, composite rotors, a composite airframe and a new transmission, Jurgens said.

The four helicopters, though for operational tests, will count toward the total contract's 200 production aircraft, and will be made where earlier test aircraft have been made: Palm Beach, Fla.